There is known a plasma processing apparatus using excitation of a processing gas by a microwave. For example, this plasma processing apparatus generates a microwave having a single frequency by using a microwave oscillator and generates plasma by radiating the microwave into a processing vessel and ionizing a processing gas within the processing vessel.
In the plasma processing apparatus using the excitation of the processing gas by the microwave, however, a reflection wave of the microwave may be generated depending on a usage condition, and a power absorbed into the plasma from the microwave may be decreased because of this reflection wave.
In this regard, there is known a technique in which a tuner for impedance matching is provided between the microwave oscillator and the processing vessel, the power of the reflection wave of the microwave is detected, and a position of a movable plate within the tuner is adjusted such that the power of the reflection wave of the microwave is minimized.